1. Field of the Invention
This invention relates to a polyol composition comprising a solid polyol which is crystalline under normal conditions and a tertiary amine containing at least two identical organic substituents, each of which has two to twenty carbon atoms. More especially, this invention relates to the prevention of caking of solid polyols and the improvement in the storability of such solid polyols under normal conditions, especially under conditions where the polyols are subjected to high pressures.
2. Discussion of Prior Art
Polyols are important intermediates for chemical synthesis, which in some cases have achieved industrial importance and are used, inter alia, for producing plastics such as polyurethanes, polycarbonates, alkyd resins, lubricants, plasticizers, lacquers and varnishes. The generally easy accessibility of polyols is a decisive factor in their wide range of uses.
Examples of technically employed polyols are 2,2-dimethyl-1,3 -propanediol (neopentyl glycol), 1,6-hexanediol and trimethylolpropane. Such polyols are prepared by catalytic hydrogenation of the corresponding carboxylic acids or esters, as in the case of 1,6-hexanediol, or mixed aldolization of aldehydes with formaldehyde and subsequent reduction of the hydroxyaldehydes, such as in the case of 2,2-dimethyl-1,3-propanediol or trimethylolpropane.
In order to ensure ease of handling during further processing, the polyols are suitably formulated and are commercially available, for example, in the form of flakes, tablets or briquettes.
The caking tendency of polyols is found to be extremely troublesome during storage. The cause of this is not always known. In the case of 2,2-dimethyl-1,3-propanediol it was found that in the solid state it exists in two different modifications, which are reversibly convertible into one another. The transformation temperatures of the thermodynamically unstable modification to the thermodynamically stable form, and vice versa, are 42.degree. C. and 33.degree. C. respectively, with supercooling. The heat of transformation of the two modifications has been calculated as 13.7 kJ/mole (H. P. Frank, K. Krzenicki, H. Vollenkle, Chemiker-Ztg. 97, 206, (1973)) and is approximately three times as great as the heat of fusion. On account of these physical properties of 2,2-dimethyl-1,3-propanediol, the production of the pure product in the form of flakes is not without problems. Difficulties arise, especially in the case of extra high quality products, which are due to the fact that the material being formulated is not completely transformed, e.g. on the flake-forming roller, into the thermodynamically more stable "low temperature modification". As a result, the neopentyl glycol subsequently changes into the corresponding "low temperature modification" in the drums and barrels for commercial sale, and the very high heat of transformation is liberated. The heat of transformation thus produces a considerable temperature rise in the product for sale and results in a more or less pronounced caking of the flaking product. In extreme cases the flow properties of the product are considerably impaired.
In order to avoid the aforementioned complications, Japanese Patent Specification 74 88 813 (CA 83, 11126 K (1975)) describes the addition of esters of organic acids or of acetals as anti-caking agents. Thus, neopentyl glycol to which 0.005% by weight of cellulose acetate butyl ester has been added, and which after formulation has been subjected for more than 30 days to a pressure of 230 p/cm.sup.2, does not exhibit any caking.
Since the described additives largely lose their effectiveness when fairly high pressures are reached, such as are produced on storage in the nowadays conventional form of fairly high stacks of sacks and bags, and moreover cause difficulties during the further processing, e.g. to form alkyd resins, polymers, lubricants and additives, the objective therefore arose of avoiding the described disadvantages and of discovering anticaking agents that are effective also under unfavorable conditions.